Yes, it is essential that the fetus does not breathe through the lungs. It is very important for the fetus, the so-called Botalla arterial duct. It connects the left artery to the aorta so that the blood passes the pulmonary vessels. With proper development, this duct closes spontaneously within 24 hours after the baby is born and the newborn takes its first breath, as it is no longer needed.
If this does not happen, blood from the left ventricle, instead of flowing into the aorta and then into the tissues of the entire body, goes to the pulmonary artery and the lungs. This is a case that the cardiologist classifies as "patent ductus arteriosus" (PDA).